1. Field of the Invention
The present invention relates to a resin composition, and more particularly to a resin composition best suited for application with a dispenser. The present invention also relates to an electronic component using the resin composition.
2. Description of the Background Art
Heretofore, there has been known a coil component configured such that a winding is attached to a drum core having a winding core portion and a pair of flange portions, and the resulting winding area is covered by a resin composition containing a thermosetting (thermally curable) resin. For example, JP 2007-67081A discloses a coil component in which a winding is wound around a drum core, and the resulting winding-wound area is covered by a resin composition comprising a mixture of a magnetic powder and a resin. A closed magnetic circuit-type coil component can be produced using such a resin composition.
Generally, a conventional resin composition for use in such a coil component is prepared to allow a viscosity thereof at room temperature to fall within a range of 50000 to 150000 mPa·s. This resin composition is injected onto several areas between the upper and lower flange portions of the drum core using a dispenser to cover the winding areas, and cured. As a prerequisite to forming a closed magnetic circuit, it is essential to seamlessly apply the resin composition onto a surface of the winding wound around the drum core so as to keep the winding from being exposed. In order to seamlessly apply the resin composition, it is necessary to inject the resin composition between the upper and lower flange portions of the drum core in a large amount, or increase the number of injection areas. Specifically, in a coil component having a size of 3 mm length×3 mm width×1 mm height, it is necessary to inject the resin composition onto 8 to 10 areas. This leads to deterioration in operating efficiency and an increase in injection amount of the resin composition.
A thermosetting resin contained in the resin composition injected into the drum core is thermally expanded when it is thermally cured or is subjected to a thermal shock test. Thus, if the resin composition is injected in a large amount, an expansion/shrinkage stress of the thermosetting resin caused by temperature changes will be imposed on the flange portions of the drum core. This is likely to cause the occurrence of crack in the drum core. Moreover, such a large injection amount of the resin composition leads to an increase in cost.
The conventional resin composition is apt to stay on an injected area due to its high viscosity and low wettability. Thus, if an injection amount of the resin composition or the number of injection areas is reduced to suppress the expansion/shrinkage stress of the thermosetting resin, it becomes difficult to seamlessly apply the resin composition onto the surface of the winding. The exposure of the winding causes not only deterioration in appearance, but also magnetic flux leakage which precludes the formation of a closed magnetic circuit to result in defective quality.
As measures against the above problems, there has been proposed a technique intended to allow a resin composition to be applied to the entire outer surface of a winding by imparting excellent fluidity to the resin composition, wherein the resin composition is prepared to have a viscosity of 10000 mPa·s or less as measured at room temperature, as disclosed in JP 3704768. However, this resin composition has poor handleability due to the significantly low viscosity at room temperature. Thus, during application with a dispenser, the resin composition is liable to attach onto a power supply terminal and a drum core.